Field of the Invention
This invention relates to an ignition control apparatus for controlling the ignition energy for igniting the mixture supplied to the internal combustion engine, in accordance with the flow velocity of the mixture flowing around the spark plug, and in particular, to an ignition control apparatus for detecting the flow velocity of the mixture in response to the rotational speed of the engine so that the ignition energy is controlled by the duration of energization of the ignition coil.
It is well known that in order to ignite the mixture supplied to the internal combustion engine, a spark plug is provided in the engine and supplied with a spark ignition voltage from the ignition coil. It is also well known that in order to accomplish highly-efficient combustion of mixture in the engine, the timing of generation of a spark ignition voltage i.e., the timing of ignition of the internal combustion engine is changed in accordance with the pressure in the engine intake pipe and the rotational speed of the engine. As one method for generating a spark ignition voltage from the ignition coil, electric power is supplied to the ignition coil from a power supply such as a battery thereby to store electric energy in the ignition coil, so that the ignition coil is de-energized at a timing in accordance with the engine operating conditions. According to this method, the spark ignition voltage is changed with the electric energy stored in the ignition coil, and therefore the ignition energy generated at the spark plug is also changed with the electric energy stored in the ignition coil. In other words, the ignition energy increases with the duration of energization of the ignition coil. If the duration of energization of the ignition coil is short, the amount of heat generated by the ignition coil is desirably small while ignition energy large enough to ignite the mixture fails to be produced. If the duration of energization of the ignition coil is long, on the other hand, a sufficiently large ignition energy is obtained while the amount of heat generated is large. One of the methods for obviating the problems associated with the duration of energization is by maintaining the ignition energy constant by maintaining the duration of energization constant.
The air-fuel mixture supplied to the internal combustion engine flows in the combustion chamber in the compression stage at a flow velocity which is higher, the higher the rotational speed of the engine. Especially in the case of an internal combustion engine having a main combustion chamber of large capacity and an auxiliary combustion chamber of smaller capacity communicating with each other, in which the mixture ignited in the auxiliary combustion chamber is spouted into the main combustion chamber, the flow velocity of the mixture transferred from the main combustion chamber into the auxiliary combustion chamber is greatly increased with the increase in the rotational speed of the engine.
The experiments conducted by the inventors show that the minimum ignition energy required for igniting completely the mixture in the combustion chamber is changed with the flow velocity of the mixture in the combustion chamber. Therefore, the above-mentioned method in which the ignition energy is maintained constant by maintaining the duration of energization constant regardless of the operating conditions of the internal combustion engine is not proper for preventing the overheating of the ignition coil and power loss by limiting the ignition energy to a required minimum.